V4L/DVB (13557): v4l: Remove unneeded video_device::minor usage in drivers

The video_device::minor field is used where it shouldn't, either to

- test for error conditions that can't happen anymore with the current
  v4l-dvb core,
- store the value in a driver private field that isn't used anymore,
- check the video device type where video_device::vfl_type should be
  used, or
- create the name of a kernel thread that should get a stable name.

Remove or fix those use cases.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>